ISIS Segment Routing IPv6 (SRv6) with FRR

This post describes the ISIS Segment Routing IPv6 (SRv6) with FRR (FRRouting) and Ubuntu (WSL).

Code repositories

Credits:
Code authours: Carmine Scarpitta and Dmytro Shytyi.
[PART1] SRv6 multiple segs SIDs series of patches
[PART2] ISIS SRv6 series of patches

I would like to thank for a review: @cscarpitta @pushpasis @donaldsharp @routingrocks and @riw777.

Linux support

Ubuntu 22.04 within WSL was used for the testbed with kernel that has activated LW_TUNNELs (CONFIG_IPV6_SEG6_LWTUNNEL)

root@munet:/# uname -a
Linux munet 5.15.90.4-microsoft-standard-WSL2+ #1 SMP Fri Jul 28 00:56:47 CEST 2023 x86_64 x86_64 x86_64 GNU/Linux

Consider to activate Sysfs variable such as “Seg6 seg6_enabled” and/or “sysctl -w net.ipv6.conf.all.forwarding=1”.

FRR configuration

r1:

!
ipv6 route 2001:db8::/64 r1-r4 segs fc00:0:6::/fc00:0:5::/fc00:0:4::
!
interface lo
 ip address 1.1.1.1/32
 ip router isis 1
 ipv6 address fc00:0:1::1/128
 ipv6 router isis 1
 isis passive
exit
!
interface r1-r2
 ip address 10.0.1.1/24
 ip router isis 1
 ipv6 router isis 1
 isis hello-multiplier 3
exit
!
interface r1-r4
 ip address 10.0.4.1/24
 ip router isis 1
 ipv6 router isis 1
 isis hello-multiplier 3
exit
!
router isis 1
 is-type level-1
 net 49.0000.0000.0000.0001.00
 lsp-timers gen-interval 2 refresh-interval 900 max-lifetime 1200
 topology ipv6-unicast
 segment-routing srv6
  locator loc1
exit
!
segment-routing
 srv6
  locators
   locator loc1
    prefix fc00:0:1::/48 block-len 32 node-len 16 func-bits 16
   exit
   !
  exit
  !
 exit
 !
exit
!
end

r2:

interface lo
 ip address 2.2.2.2/32
 ip router isis 1
 ipv6 address fc00:0:2::1/128
 ipv6 router isis 1
 isis passive
exit
!
interface r2-r1
 ip address 10.0.1.2/24
 ip router isis 1
 ipv6 router isis 1
 isis hello-multiplier 3
exit
!
interface r2-r3
 ip address 10.0.2.2/24
 ip router isis 1
 ipv6 router isis 1
 isis hello-multiplier 3
exit
!
router isis 1
 is-type level-1
 net 49.0000.0000.0000.0002.00
 lsp-timers gen-interval 2 refresh-interval 900 max-lifetime 1200
 topology ipv6-unicast
 segment-routing srv6
  locator loc1
exit
!
segment-routing
 srv6
  locators
   locator loc1
    prefix fc00:0:2::/48 block-len 32 node-len 16 func-bits 16
   exit
   !
  exit
  !
 exit
 !
exit
!
end

…

r7:

!
interface lo
 ip address 7.7.7.7/32
 ip router isis 1
 ipv6 address fc00:0:7::1/128
 ipv6 router isis 1
 isis passive
exit
!
interface r7-r3
 ip address 10.0.3.7/24
 ip router isis 1
 ipv6 router isis 1
 isis hello-multiplier 3
exit
!
interface r7-r6
 ip address 10.0.7.7/24
 ip router isis 1
 ipv6 router isis 1
 isis hello-multiplier 3
exit
!
router isis 1
 is-type level-1
 net 49.0000.0000.0000.0007.00
 lsp-timers gen-interval 2 refresh-interval 900 max-lifetime 1200
 topology ipv6-unicast
 segment-routing srv6
  locator loc1
exit
!
segment-routing
 srv6
  locators
   locator loc1
    prefix fc00:0:7::/48 block-len 32 node-len 16 func-bits 16
   exit
   !
  exit
  !
 exit
 !
exit
!
end

Display SRv6 route on r1

FRR:

r1# show ipv6 route
Codes: K - kernel route, C - connected, S - static, R - RIPng,
       O - OSPFv3, I - IS-IS, B - BGP, T - Table, v - VNC,
       V - VNC-Direct, A - Babel, F - PBR, f - OpenFabric,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

S>* 2001:db8::/64 [1/0] is directly connected, r1-r4, seg6 fc00:0:6::,fc00:0:5::,fc00:0:4::, weight 1, 01:52:08
[..]

iproute2:

root@r1:/# ip -6 route
2001:db8::/64 nhid 41  encap seg6 mode encap segs 3 [ fc00:0:4:: fc00:0:5:: fc00:0:6:: ] dev r1-r4 proto 196 metric 20 pref medium

Display ISIS SRv6 seg6local behavior on R2

The same seg6local behavior is bootstrapped on r3, r4, r5, r6, r7 nodes.

r2 router:

r2# show ipv6 route
Codes: K - kernel route, C - connected, S - static, R - RIPng,
       O - OSPFv3, I - IS-IS, B - BGP, T - Table, v - VNC,
       V - VNC-Direct, A - Babel, F - PBR, f - OpenFabric,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure
[..]
I>* fc00:0:2::/128 [115/0] is directly connected, sr0, seg6local End USP, weight 1, 02:34:25

r5 router:

r5# show ipv6 route
Codes: K - kernel route, C - connected, S - static, R - RIPng,
       O - OSPFv3, I - IS-IS, B - BGP, T - Table, v - VNC,
       V - VNC-Direct, A - Babel, F - PBR, f - OpenFabric,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

[..]
I>* fc00:0:5::/128 [115/0] is directly connected, sr0, seg6local End USP, weight 1, 02:37:17

Testbed consoles presented with routers indexes

This figure (if font is too small, please open figure in new separate window) is related to the network topology presented in the top of article. This figure describes router placement that doesn’t change in future figures.
Also you may find parts of configuration presented in rectangles.

Testbed – echo request/reply based on ISIS SPF (RED Line in the first figure)

This figure (if font is too small, please open figure in new separate window) is related to the network topology presented in the top of article. This figure describes the echo “request”/”reply” process in regular setup. Echo request is sent via SPF (r1-r2-r3-r7) – red line in the fist figure. Echo reply is returned in vise-versa manner.

Testbed – echo request/reply based with SRv6 features (Blue SRv6 Low-Latency tunnel)

This figure (if font is too small, please open figure in new separate window) is related to the network topology presented in the top of article. This figure describes the echo “request”/”reply” process witch SRv6 features.
Echo request is sent via the low-latency path (r1-r4-r5-r6-r7) using the SRv6 route and returned by regular path (r7-r3-r2-r1).

Publication date: 07/28/2023 3:57AM